//Parses a label into a C-string containing a dotted
//Returns pointer to start of next fields in packet
static char* labelToStr(char *packet, char *labelPtr, int packetSz, char *res, int resMaxLen) {
int i, j, k;
char *endPtr=NULL;
i=0;
do {
if ((*labelPtr&0xC0)==0) {
j=*labelPtr++; //skip past length
//Add separator period if there already is data in res
if (i<resMaxLen && i!=0) res[i++]='.';
//Copy label to res
for (k=0; k<j; k++) {
if ((labelPtr-packet)>packetSz) return NULL;
if (i<resMaxLen) res[i++]=*labelPtr++;
}
} else if ((*labelPtr&0xC0)==0xC0) {
//Compressed label pointer
endPtr=labelPtr+2;
int offset=local_ntohs(((uint16_t *)labelPtr))&0x3FFF;
//Check if offset points to somewhere outside of the packet
if (offset>packetSz) return NULL;
labelPtr=&packet[offset];
}
//check for out-of-bound-ness
if ((labelPtr-packet)>packetSz) return NULL;
} while (*labelPtr!=0);
res[i]=0; //zero-terminate
if (endPtr==NULL) endPtr=labelPtr+1;
return endPtr;
}
//Receive a DNS packet and maybe send a response back
static void captdnsRecv(struct sockaddr_in *premote_addr, char *pusrdata, unsigned short length) {
int i;
char *buff = (char*)zalloc(DNS_LEN);
char *reply = (char*)zalloc(DNS_LEN);
char *rend=reply+length;
char *p=pusrdata;
DnsHeader *hdr=(DnsHeader*)p;
DnsHeader *rhdr=(DnsHeader*)reply;
p+=sizeof(DnsHeader);
// printf("DNS packet: id 0x%X flags 0x%X rcode 0x%X qcnt %d ancnt %d nscount %d arcount %d len %d\n",
// local_ntohs(&hdr->id), hdr->flags, hdr->rcode, local_ntohs(&hdr->qdcount), local_ntohs(&hdr->ancount), local_ntohs(&hdr->nscount), local_ntohs(&hdr->arcount), length);
//Some sanity checks:
if (length>512) goto finish; //Packet is longer than DNS implementation allows,512
if (length<sizeof(DnsHeader)) goto finish; //Packet is too short
if (hdr->ancount || hdr->nscount || hdr->arcount) goto finish; //this is a reply, don't know what to do with it
if (hdr->flags&FLAG_TC) goto finish; //truncated, can't use this
//Reply is basically the request plus the needed data
memcpy(reply, pusrdata, length);
rhdr->flags|=FLAG_QR;
for (i=0; i<local_ntohs(&hdr->qdcount); i++) {
//Grab the labels in the q string
p=labelToStr(pusrdata, p, length, buff, DNS_LEN);
if (p==NULL) goto finish;
DnsQuestionFooter *qf=(DnsQuestionFooter*)p;
p+=sizeof(DnsQuestionFooter);
printf("DNS: Q (type 0x%X class 0x%X) for %s\n", local_ntohs(&qf->type), local_ntohs(&qf->class), buff);
if (local_ntohs(&qf->type)==QTYPE_A) {
//They want to know the IPv4 address of something.
//Build the response.
rend=strToLabel(buff, rend, DNS_LEN-(rend-reply)); //Add the label
if (rend==NULL) goto finish;
DnsResourceFooter *rf=(DnsResourceFooter *)rend;
rend+=sizeof(DnsResourceFooter);
setn16(&rf->type, QTYPE_A);
setn16(&rf->class, QCLASS_IN);
setn32(&rf->ttl, 0);
setn16(&rf->rdlength, 4); //IPv4 addr is 4 bytes;
//Grab the current IP of the softap interface
struct ip_info info;
wifi_get_ip_info(SOFTAP_IF, &info);
*rend++=ip4_addr1(&info.ip);
*rend++=ip4_addr2(&info.ip);
*rend++=ip4_addr3(&info.ip);
*rend++=ip4_addr4(&info.ip);
setn16(&rhdr->ancount, local_ntohs(&rhdr->ancount)+1);
// printf("Added A rec to resp. Resp len is %d\n", (rend-reply));
} else if (local_ntohs(&qf->type)==QTYPE_NS) {
static PyObject *
parse_tuple_message(PyObject *self, PyObject *args)
{
PyObject *prerob, *rob, *temp_tup;
PyObject *typ;
const char *data;
Py_ssize_t dlen = 0;
uint16_t natts = 0;
if (!PyArg_ParseTuple(args, "Oy#", &typ, &data, &dlen))
return(NULL);
if (dlen < 2)
{
PyErr_Format(PyExc_ValueError,
"invalid tuple message: %d bytes is too small", dlen);
return(NULL);
}
memcpy(&natts, data, 2);
natts = local_ntohs(natts);
prerob = PyTuple_New(natts);
if (prerob == NULL)
return(NULL);
if (_unpack_tuple_data(prerob, natts, data+2, dlen-2) < 0)
{
Py_DECREF(prerob);
return(NULL);
}
temp_tup = PyTuple_New(1);
if (temp_tup == NULL)
{
Py_DECREF(prerob);
return(NULL);
}
PyTuple_SET_ITEM(temp_tup, 0, prerob);
rob = PyObject_CallObject(typ, temp_tup);
Py_DECREF(temp_tup);
return(rob);
}
